1. Field of the Invention
The present invention relates to a display panel, and more particularly to a display panel with a reduced number of connections.
2. Description of the Prior Art
Known as a typical active matrix circuit board is a liquid crystal display device using TFTs (Thin-film-Transistors) as switching elements. Liquid crystal display devices have drawn attention as a substitute for CRT display devices. To meet the recent requirements for high resolution and high quality, the number of scanning lines reaches as many as several hundreds, and the circuit density is high.
FIG. 2 shows a circuit construction of a conventional active matrix type liquid crystal display device. In the figure, reference numeral 1 denotes a display unit 1, reference A.sub.NM denotes a TFT switching element for driving a pixel, reference numeral 2 denotes a signal line drive circuit, reference numeral 3 denotes a scanning line drive circuit, and reference numeral 4 denotes a connection point between the display unit 1 and the scanning line drive circuit 3. References G(1) to G(N) represent scanning lines, and references S(1) to S(M) represent signal lines. If a matrix arrangement N.times.M (N and M are positive integers) is employed for such a display device to connect N scanning lines and M signal lines, the number of connection points 4 becomes N. As to the circuit density, a compact liquid crystal television is here taken as an example which has 480 scanning lines, aspect ratio of 3:4, and diagonal screen size of 3 inches. In this case, since the vertical length l of the screen is: EQU l=3.times.25.4 (mm).times.(3/5).apprxeq.46 (mm)
the density d of scanning lines is: EQU d=(N/l)=(480/46).apprxeq.10.4 (line/mm)
which shows a density of about 10 lines per 1 mm.
Under the necessity of connecting to a plural number of scanning lines of high density to an external scanning line drive circuit, there have been some problems that reliability and yield in implementing such a device is low and cost is expensive. Furthermore, since the scanning line drive circuit requires N output lines, the circuit becomes bulky and expensive.